There is known a conventional glass package type capacitive device in which a dielectric film is formed on a surface of a silicon substrate to form a capacitive element and the capacitive element is sealed within a glass container (refer to a Japanese Patent Publication No. 57-26432). This type of capacitive devices have been widely used because the element can be easily made in a microminiaturized form at a high production speed and also can have characteristic values conforming to design values.
In this capacitive device, as shown in FIG. 3, a capacitive element 2 formed of a silicon chip is sealed within a cylindrical glass container 1 and leads 5 and 6 are led out from electrodes 3a and 3b of the capacitive element 2 through solder layers 4a and 4b respectively. Reference numerals 7a and 7b denote a silicon nitride film and a silicon oxide film formed on a surface of a silicon substrate to form a dielectric film by this two-layered film. The electrode 3a is disposed on this dielectric film.
In such a capacitive device, the dielectric film formed on the silicon substrate is as thin as at most several .mu.m. However, when it is desired to obtain a large capacitance, the thin film is sometimes formed to have a thickness of about 10 nm. In the latter case, there is a problem that the device becomes weak when subjected to an external stress.
Further, since a high temperature of 600.degree.-800.degree. C. is required for the glass sealing, when returned to a room temperature, thermal stresses within the glass container cannot escape from inside of the glass container to outside, which means that a stress caused by a difference in expansion coefficients is applied directly to the dielectric film. For this reason, with respect to relatively soft films having a low denseness, that is, insulating films such as silicon oxide films or titanium oxide films formed by a liquid phase growth technique, insulating films formed by a physical vapor phase growth process as a sputtering process or an electron beam vapor deposition process, or insulating films (spin-on glass) made from an alcoholic solution of silanol as its major material, it is highly difficult to assemble or fabricate such a film by a conventional sealing method while maintaining its normal characteristics. Even such a film that is considered to be relatively soft and resistive to stress as a silicon oxide film formed by a thermal oxidation method, a silicon nitride film formed by a plasma chemical vapor deposition (CVD) process, or a composite film thereof, has a problem that such a film, in many cases, tends, to be destroyed or deteriorated in its characteristics by thermal stress during its fabrication.
Further, even when such a film is successfully fabricated into its normal state, there is a problem that the film is susceptible to a drop shock or a thermal shock caused at the time of soldering the element to a circuit substrate.